Optoelectrical distance meters (also referred to as EDMs (electronic distance meters, LRFs (laser rangefinders), LIDAR, etc.) operate on the principle of emitting electromagnetic radiation, usually in the form of pulses of visible or invisible light, in the direction of a target object. This target object sends at least a part of the emitted light back in the direction of the measuring instrument, in which this received light is converted into an electrical signal. With the aid of the required time of flight of the light and the known propagation speed of the light, the distance between the measuring instrument and the target object is determined by an electronic evaluation unit.
Exemplary embodiments of such instruments are to be found, for instance, in Documents EP 2 051 102, EP 1 311 873 or EP 1 913 415, in which further details of the measurement principles may also be found.
The emission of the light should in this case be carried out as a light beam with the smallest possible divergence, for example in order to obtain a clearly defined measurement point on the target object, as well as to keep the light signal intensity at the measurement point high even in the case of large measurement distances, and inter alia also to obtain a clearly visible measurement point on the target object when using visible light.
In order to obtain such a light beam with small divergence, corresponding collimation optics or emission optics are provided, which need to be adjusted accordingly relative to the light source in order to achieve the desired beam divergence. Semiconductor light sources such as laser diodes or LEDs are preferably used as the light sources, laser emitters being used most often owing to their generically small beam divergence. The collimation optics may be configured as a simple optical lens, or alternatively as more complex optics. Owing to manufacturing tolerances, particularly in the case of large measurement distances, it may be necessary to adjust the collimation optics separately for each instrument in the scope of the manufacturing process of the EDM.
Also when receiving the light, reception optics, for example a converging lens, are mostly used which focus the light from the target object direction onto a photosensitive component, for example a photodiode, especially a PIN photodiode or APD. In this way, the light-receiving cross-sectional area of the instrument, with which the light sent back is acquired, can be increased in relation to the relatively small light-sensitive region of the photosensitive component. The intensity of the optical signal on the receiver element can be increased by a large aperture of the reception optics. The active areas of the photosensitive component usually need to be kept small for other reasons, for example in order to avoid saturation by ambient light, and also since the reaction time or bandwidth of the receiver decreases with an increase in the active area.
The reception optics also need to be oriented in terms of their focus relative to the electro-optical reception element, larger dimensional tolerances usually being permissible in this case than when collimating the emitter. The main purpose of the reception lens is to collect the received light, an exact sharp image of the target on the receiver not being absolutely necessary.
Both the emission optics and the reception optics may also comprise further optical components besides the aforementioned lenses: for instance wavelength filters, polarization filters, deviating mirrors, etc.
Besides the adjustment of the focusing of the emission and reception optics, the optical axes of the emission and reception beam paths are also to be oriented with respect one another in such a way that the part of the emitted light sent back from the target object actually strikes the receiver. This must be ensured over the entire specified measurement range of the EDM, and requires that the respective two angular directions of the two beam paths are appropriately oriented with respect to one another. The solution of a coaxial emission beam path and reception beam path fulfills this criterion; the optical components required for this are, however, very elaborate. EDMs, in particular simple handheld distance meters, are therefore usually not configured with coaxial beam paths, but instead the emission and reception optics are arranged next to one another. In order to satisfy the orientation conditions, the optical axes of the emission and reception beam paths must at least approximately intersect at a point which lies at a particular distance and not at infinity.
For the reasons mentioned above, adjustment of an emission element, emission optics, reception optics and a reception element with respect to one another is necessary in the scope of EDM manufacture. To this end, when assembling the instrument in the prior art, the emission and reception elements are respectively adjusted separately in terms of their position relative to the associated optics. This, however, means that the emitter cannot be positioned in a fixed way relative to the receiver—at least during the adjustment. For example, the emitter and receiver cannot therefore already be fixed and definitively positioned beforehand on a common prefabricated printed circuit board.
For example, Document EP 1 351 070 is known, in which adjustment of the beam path of a distance meter is carried out by temporarily making the photodiode adjustable in position by means of its electrical contacts and is electrically conductively fixed in its adjusted position on the printed circuit board after the adjustment has been carried out. In other words, for example, a solder point of the photodiode is melted and the photodiode is thus made temporarily movable for the adjustment. In EP 1 752 788, the receiver is rigidly connected to the printed circuit board in at least two directions.
WO 2007/012531 or WO 2007/033860 also disclose distance meter structures and describe their adjustment by movement of the emitter and/or receiver, which are fitted on different printed circuit boards or which (at least during the adjustment) are made movable relative to the printed circuit board. DE 101 57 378 discloses a distance meter having a temperature-compensated arrangement of the optical axes. In EP 1 980 878, emission and reception optics are connected to form a double lens.
For orientation of the optical axes of emission and reception paths, as an alternative optics are also known which are configured displaceably or tiltably relative to the printed circuit board with a fixed emission element and a fixed reception element. Such a mechanical structure, however, proves to be elaborate in design. For example, two optics carriers movable with respect to one another, for emission and reception optics, would impair the mechanical robustness of the EDM system. Adhesive bonding of freely movable adjustable optics in an accurately adjusted position also proves correspondingly difficult and error-prone in the scope of EDM manufacture.